736 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1957 



The data were adjusted to correct for the errcjr introduced in this 

 manner, so that open loop conditions are represented. The etiualization 

 networks have compensating leading characteristics to prevent the oscil- 

 lation suggested by the increasing phase shift at the higher frefiuencies. 



If the servo acted in strict accordance \\ ith minimum-phase network 

 theory, the slope of the gain curve would have started to increase at the 

 high frequenc}^ end of Fig. 19. The effects of nonlinearities caused by 

 such things as overlap and dither action cause this departure from 

 classical theory. Actually, the slope does start toward 12 db per octave 

 just above the frequency range shown. 



Part of the phase shift shown on Fig. 19 is due to the inductance of the 

 coils and the relatively low source impedance of the amplifier used. Later 

 amplifier designs have much higher output impedance, which has 

 greatly reduced this effect. 



CONCLUSION 



The series of hydraulic valves developed for use in the NIKE missile 

 provide a light-weight, high-performance control element for positioning 

 aerodynamic control surfaces. Although these electrohydraulic trans- 

 ducers provide a high power amplification, they are relatively simple 

 single-stage devices. Their successful application in the XIKE missile 

 has caused hydraulic servos to be considered for many other military 

 control systems, some of which are under active development at this 

 time. The hydraulic servo has many advantages to offer in the high 

 power field that cannot be provided by other conventional types. It is 

 expected that these advantages will foster a great increase in the use of 

 hydraulic servos in high performance applications in the next few years. 



ACKNOWLEDGMENT 



The writer wishes to thank E. L. Norton w^ho contributed greatly to all 

 phases of the valve development and V. F. Simonick of the Douglas 

 Aircraft Company who provided valuable consultation on the hydraulic 

 problems involved. 



REFERENCES 



1. Peek, R. L. and Wagar, H. N., Magnetic Design of Relays, B. S.T.J. , Jan., 1954. 



2. Ekelof, Stig, Magnetic Circuit of Telephone Relays — A Study of Telephone 



Relays — I, Ericsson Technics, 9, No. 1, pp. 51-82, 1953. 



3. Von Mises, R., Berechnung von Ausfluss — and Ueberfallzahlen, Zeitschrift 



des Vereines Deutscher Ingenieure, 61, pp. 447-452, 469-474, 493-498, Mav- 

 June, 1917. 



4. Lee, Shih-Ying, and Blackburn, John F., Axial Forces on Control-Valve Pis- 



tons, Meteor Report No. 65, Mass. Inst, of Tech., Jvuie, 1950. 



5. Holoubeck, F., Free Oscillations of Valve-Controlled Hydraulic Servos, Royal 



Aircraft Establishment, Technical Note Mechanical Engineering-100, Nov., 

 1951. 



